This invention relates to stackable shipping containers for flowable substances and, more particularly, to heavy-duty stackable shipping containers for the bulk transport of flowable bulk materials. As used herein the term "heavy-duty shipping container" shall mean a container for bulk materials including liquids, dry powders or granular substances, semi-solid materials such as grease, pastes or adhesives and, as well, highly viscous fluids, in volumes of at least fifty-five gallons and in weight greater than four hundred-fifty pounds.
Shipping containers used for the transport of flowable bulk materials must accommodate extraordinary weight, due to the high density of the contained materials and, at the same time, must be designed to withstand damage that can result from the nonuniform and sometimes cyclic stresses caused by the material shifting during the handling and transport of the container. Even a minor puncture or crack can cause the total loss of the flowable material. Heavy-duty shipping containers containing bulk flowable materials exceed the limits of manual handling capability and are typically mounted on pallets and handled by mechanical means such as fork lifts and handlift trucks.
Various types of containers and container materials have been designed for the transport of flowable bulk materials. Single wall (double face) corrugated fibreboard boxes, for example, have been used as inexpensive, disposable containers for light-duty applications. Such fibreboard containers, where necessary, are waxed or provided with a plastic liner bag. As the volume and weight of the contained material increases, however, the pressure of the material within the container causes bulging of the sides of the container. This makes the container difficult to stack with other similar containers. Furthermore, the bulging of the sides of the container significantly reduces the inherently limited column strength of single wall containers making this type of container unsuitable for stacking or heavy-duty application.
The term fibreboard is a general term applied to paperboard utilized in container manufacture. Paperboard refers to a wide variety of materials most commonly made from wood pulp or paper stock. Containerboard refers to the paperboard components--liner and corrugating material--from which corrugated fibreboard is manufactured. Thus, the term fibreboard, as used in the packaging industry and in the present specification and claims, is intended to refer to a structure of paperboard material composed of various combined layers of containerboard in sheet and fluted form to add rigidity to the finished product. Fibreboard is generally more rigid than other types of paperboard, allowing it to be fabricated into larger sized boxes that hold their shape and have substantial weight bearing capability.
Double or triple wall corrugated fibreboard, when made into shipping containers, provides many distinct advantages for the packaging and transport of heavy loads. Double wall corrugated fibreboard comprises two corrugated sheets interposed between three flat facing or spaced liner sheets. In triple wall corrugated fibreboard, three corrugated sheets are interposed between four spaced facing or liner sheets. Triple wall corrugated fibreboard, in particular, compares favorably with wood in rigidity and strength and, as well, in cost, and provides cushioning quality not found in wooden containers. In addition, triple wall corrugated fibreboard, relative to other fibreboard materials, advantageously provides great column strength. The column strength of triple wall corrugated fibreboard containers permits stacking, one on top of the another, of containers containing heavy loads without excessive buckling or complete collapse of the vertical walls. Triple wall corrugated fibreboard also has great resistance against tearing.
Fibreboard shipping containers employing an outer multi-sided tubular member and a simularly configured inner reinforcement to strengthen the overall container have been disclosed. See, for example, U.S. Pat. Nos. 3,159,326; 3,261,533; 3,873,017; 3,937,392; 4,013,168 and; 4,418,861.
In order to form multi-sided fibreboard tubes, it is necessary to form major score lines in the fibreboard to allow bending of the fibreboard along the edges of each panel of the container which is formed. However, scoring adversely affects the container since the lateral stability of the container significantly decreases as the number of major score lines is increased. The major scoring of the container typically permits the container, when empty, to be shipped in a knocked down, flat condition.
Circular cylindrical-shaped containers have long been regarded as the most efficient shape to use in containing liquids or dry flowable products. Paperboard designs utilizing circular cylindrical type containers, however, have been restricted to small capacity cylindrical shapes typlified by the 55 gallon capacity spiral wound fibre drum. Producing larger containers of this type has proven impractical, on a commercial basis, due to a number of reasons including excessive material and fabrication costs and the unavailability of fabricating equipment. Moreover, the fibre drums are rigid and cannot be folded into a flattened state when empty. Since existing technology requires that these fibre drums be preerected at a central location and then shipped to and stored empty in an erected or pre-formed condition at user locations, the utilization of cylindrical fibre drums also presents handling, shipping, and storing difficulties. Most importantly, the structural performance and handling requirements of a fibre drum, as capacity climbs to the 110 gallon to 380 gallon range, have exceeded the industry's ability to produce a readily available commercial product. Utilization of higher-strength reinforced plastic or metal drums has not provided a satisfactory alternative as such materials are typically more expensive, do not increase utilization of cubic storage space, when empty, and present a variety of disposal problems.
Thus, despite the efficiencies of circular cylindrical containment, corrugated fibreboard has not been generally used as a circular cylindrical container material. Corrugated fibreboard, particularly in the heavier grades of multi-wall fibreboard capable of containing and supporting the weights and hydrostatic pressures produced by 110 to 380 gallons of contained liquid, or an equal volume and weight of flowable solids, does not lend itself to being fabricated into circular cylindrical shapes without substantial loss of key performance features of corrugated fibreboard, that is, top to bottom compression strength and lateral stability.